System And Method Of Implementing Lightweight Not-Via IP Fast Reroutes In A Telecommunications Network

ABSTRACT

A system, method, and node for implementing lightweight Not-via Internet Protocol fast reroutes of a packet in a telecommunications network between a first node and a destination node. The method determines a shortest path between the first node and the destination node and two redundant trees between the first node and the destination node. Each redundant tree provides an alternate path from the first node and the destination node. When a failure in a link between the first node and the destination node is detected, the packet is forwarded to the destination node via a first redundant tree, and if not available, via a second redundant tree. If the second redundant tree is not available, the packet is dropped. If no failure in the link between the first node and the destination node is detected, the packet is sent via the determined shortest path to the destination node.

TECHNICAL FIELD

The present invention relates generally to communications networks, andin particular, to a system and method of implementing lightweightNot-Via IP fast reroutes in a telecommunications network.

BACKGROUND

When using the traditional resilience methods in Internet Protocol (IP)networks, the re-routing of traffic around a failure can take asignificant time. A primary reason for this slow reconfiguration is thereactive approach offered by conventional routing protocols, such asOpen Shortest Path First (OSPF) or the IntermediateSystem-to-Intermediate System (IS-IS) routing protocol, which are widelydeployed in modern IP networks. With existing protocols, fault recoveryis assured by propagating the information about the failure in thenetwork and re-computing the routing tables at each router. This isaccomplished after a failure exists which increases the time necessaryfor re-routing a packet.

In contrast to traditional IP error correction techniques, which arefundamentally reactive, the new IP Fast Reroute (IPFRR) frameworkstandardized in the Routing working group of Internet Engineering TaskForce (IETF) proposes proactive solutions. Thus, these methods arealways ready to reroute packets. However, the reroute must be conductedlocally through algorithms because there is no time for anycommunication. By using these algorithms, transient link errors may alsobe avoided. Since packets can reach the destination, the starting of thereconfiguration of the network can be delayed until the failure isverified.

Among the IPFRR techniques, methods using Not-via addresses areimportant in accomplishing re-routes. These methods use simple IP-in-IPtunnels to avoid a single failed resource, which is an inexpensiveoperation in current routers. The resource may be either a node or alink. If there is more than one failure, packets may not reach thedestination. In such a situation, packets may be dropped, therebypreventing the formation of a loop.

Two redundant trees may be directed at spanning trees rooted at anarbitrary given node (root node) in such a way that there is a path fromeach node to the root on both trees. These paths are ‘node-disjointed’to provide separate paths utilizing different nodes. Redundant trees canalways be found, even in linear time, if the network is two-nodeconnected. Thus, these trees may be used for resilience if thedestination is the root node. Furthermore, if the graph used in definingthe pathways of the packet is not two-node connected, two directed treesmay be found in such a way that the two paths from any of the nodes tothe root are maximally node and edge disjointed. These trees are knownas maximally redundant trees and may also be found in linear time by asimple modification of the algorithm finding redundant trees. If anetwork is two-node-connected, perfect redundancy can be achieved sincemaximally redundant trees are also redundant trees. Furthermore, it isalso possible to compute the next hops of two redundant trees. Thenecessary parts of the trees for resilience are rooted at each node as aroot in linear time.

However, there are problems with the existing methods. The reroutingtime of conventional routing protocols is too long. Studies have shownthat using OSPF or IS-IS, rerouting time can take numerous seconds orlonger in extreme cases. Gigabytes of data may be lost during this timeperiod. Additionally, users of applications or the applicationsthemselves may even lose their sessions. Obviously, for real timetraffic, such as Internet Protocol Television (IPTV) or Voice over IP(VoIP), this slow response is even more undesirable.

The greatest problem of the simplest IPFRR techniques is that they cancorrect failures only in special cases (e.g., when multiple equal costshortest paths (like in ECMP) or multiple loop free alternate pathsexist to the destination).

Currently, there are only two IPFRR methods which can provide onehundred percent link fault recovery, Failure Insensitive Routing (FIR)and Not-via Addresses. However, neither of these techniques can alwaysprovide fast resilience when more than one failure occurssimultaneously.

The original FIR is prone to create loops when more than one link or, atleast one node has failed. A loop is a forwarding cycle which is neverleft by packets. Packets are dropped when Time-To-Live (TTL) is up.There is a solution which can avoid these loops. However, when the loopsare avoided, the paths used when no failure exists must generally belonger then the shortest paths.

The existing Not-via addresses also suffers from some disadvantages.Although Not-via Addresses uses the shortest paths when no failures arepresent, numerous IP addresses are used in order to avoid a failedresource if necessary. In such circumstances, the number of IP addressesscales quadratically. This high number of IP addresses raises theproblem of managing these addresses. Furthermore, utilizing a Not-viamethod also increases the computational complexity. This method needsnumerous shortest path computations. Thus, the time needed to downloadthe computed routings to the line cards of the routers is also increasedbecause of the high number of addresses. Additionally, a Not-via methodutilizes several special cases, thereby making it difficult to debug andimplement.

SUMMARY

The present invention is a modification of the existing Not-via addresssolution. Instead of computing several shortest path trees, the presentinvention determines a pair of redundant trees (the primary and thesecondary trees) for each node as a root. Furthermore, the presentinvention determines a shortest path in the network where no failureexists. If a packet cannot be forwarded on the shortest path, the packetis placed in an IP-in-IP tunnel and is forwarded to the next-next hopalong the primary redundant tree. If a node cannot forward the packet onthe primary tree, the packet is forwarded on the secondary tree.

Thus, in one embodiment, the present invention is directed to a methodof implementing lightweight Not-via Internet Protocol fast reroutes of apacket in a telecommunications network between a first node and adestination node. The method includes the steps of determining ashortest path between the first node and the destination node anddetermining first and second redundant trees between the first node andthe destination node. Each redundant tree provides an alternate pathfrom the first node and the destination node. When a failure in a linkexists between the first node and the destination node is detected, thepacket is forwarded to the destination node via the first redundant treeif the first redundant tree is available. If the first redundant tree isnot available, the packet is forwarded to the destination node via thesecond redundant tree if the second redundant tree is available. If thesecond redundant tree is not available, the packet is dropped. If nofailure in the link between the first node and the destination node isdetected, the packet is sent via the determined shortest path to thedestination node.

In another embodiment, the present invention is directed to a system forimplementing lightweight Not-via Internet Protocol fast reroutes of apacket in a telecommunications network. The system includes a first nodetransmitting a packet and a destination node for receiving the packet.The first node determines a shortest path between the first node and thedestination node and also determines first and second redundant treesbetween the first node and the destination node. The redundant treesprovide alternate paths from the first node and the destination node.The first node determines if a failure in a link exists between thefirst node and the destination node and, upon determining a failureexists between the first node and the destination node, forwards thepacket via the first redundant tree to the destination node. If thefirst redundant tree is not available, the packet is forwarded to thedestination node via the second redundant tree if the second redundanttree is available. If the second redundant tree is not available, thepacket is dropped. If no failure in the link between the first node andthe destination node is detected, the packet is sent via the determinedshortest path to the destination node.

In still another embodiment, the present invention is directed to a nodefor implementing lightweight Not-via Internet Protocol fast reroutes ofa packet in a telecommunications network from the node to a destinationnode. The node determines a shortest path between the node and thedestination node and determines first and second redundant trees betweenthe node and the destination node. The redundant trees provide alternatepaths between the node and the destination node. The node alsodetermines if a failure in a link exists between the first node and thedestination node and, upon determining a failure exists between thefirst node and the destination node, forwards the packet via the firstredundant tree to the destination node. If the first redundant tree isnot available, the packet is forwarded to the destination node via thesecond redundant tree if the second redundant tree is available. If thesecond redundant tree is not available, the packet is dropped. If nofailure in the link between the first node and the destination node isdetected, the packet is sent via the determined shortest path to thedestination node.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) illustrates a simplified block diagram of anexemplary Universal Mobile Telecommunications Systems network;

FIG. 2 is a simplified diagram illustrating the pathways fortransmitting packets in a system in an embodiment of the presentinvention; and

FIGS. 3A and 3B are flowcharts illustrating the steps of forwarding apacket where a node or link failure occurs in a network according to theteachings of the present invention.

DETAILED DESCRIPTION

The present invention is a system and method of implementing lightweightNot-Via IP Fast Reroutes in a telecommunications network. The presentinvention is a modification of the existing Not-via address solution. Inthe present invention, tunnelling is utilized to send packets on adetour. In a similar manner as the existing Not-via address solution,tunnelling is accomplished by using special IP addresses (e.g., privateaddress such as 10.0.0.0/24). However, in the present invention,significantly less IP addresses are needed, thereby loweringcomputational complexity of the system.

In the present invention, rather than computing several shortest pathtrees, a pair of redundant trees (the primary and the secondary trees)is computed for each node as a root. Additionally, one shortest path inthe network with no failures is also computed. In a similar manner asexisting Not-via solutions, the default path for a packet is theshortest path. If a packet cannot be forwarded on the shortest path, anIP-in-IP tunnel is implemented. However, unlike the existing Not-viaaddress solution, the packet is forwarded to the next-next hop along theprimary redundant tree. If a router or node cannot forward the packet onthe primary tree, the packet is forwarded on the secondary tree. If thepacket reaches the next-next hop, the tunnel remains intact and thepackets follow the shortest path as usual.

Thus, the packet can reach the destination if a single node or linkfails since one of the redundant trees remains untouched by the failure.In the present invention, a node only needs three IP addresses. Thepresent invention may be scaled linearly with any number of nodes. In ageneral network, where all the interfaces have their own addresses, noextra IP address is necessary. In addition, three IP addresses per nodeis the minimum reachable by the original Not-via addresses. However, inan illustrated embodiment, the present invention is implemented inpoint-to-point networks with ring topology. Computing the next hops ofredundant trees may be accomplished in linear time so the computationalcomplexity of the present invention is equal to the complexity of asingle Dijkstra algorithm.

FIG. 1 illustrates a simplified block diagram of an exemplary UniversalMobile Telecommunications Systems (UMTS) network 100 that comprises a3^(rd) Generation (3G) network referred to as a core network 102 and aUMTS Terrestrial Radio Access Network (UTRAN) 104. The UTRAN comprises aplurality of Radio Networks Controllers (RNCs) 106. In addition, thereis a plurality of RNCs performing various roles. Each RNC is connectedto a set of base stations. A base station is often called an eNodeB.Each eNodeB 108 is responsible for communication with one or more UserEquipments (UEs) 110 within a given geographical cell. The serving RNCis responsible for routing user and signaling data between an eNodeB andthe core network. FIG. 1 illustrates a network which may be utilized inthe present invention. However, the present invention may be implementedon any packet-switched network and is not limited to the networkconfiguration illustrated in FIG. 1.

FIG. 2 is a simplified diagram illustrating the pathways fortransmitting packets in a system 200 in an embodiment of the presentinvention. The system 200 includes a plurality of nodes 0, 1, 2, 3, 4,and 5. Pathways 202, 204, 206, 208, and 210 illustrate the shortest pathtree to the node 0. Pathways 220, 222, 224, 226, and 228 illustrate theprimary redundant tree rooted at node 1. Pathways 230, 232, 234, 236,and 238 illustrate the second redundant tree rooted at node 1. Asdepicted in FIG. 2, if there are no failure in the network, node 5 sendspackets to node 0 on a sequential path through nodes 5-3-1-0. However,if node 3 fails, node 5, a neighbor of node 3, detects the failure andtries to send the packet to the next-next hop (i.e., node 1) in anIP-in-IP tunnel. To forward this packet, node 5 first tries to utilizethe primary redundant tree, but determines that it is also failed.However, the network may utilize the secondary redundant tree. Thus,node 5 sends the packet to node 4 via pathway 230. Node 4 detects thatthe packet is on the secondary redundant tree of node 1 from thedestination address, so node 4 then tries to forward the packet on thesame secondary redundant tree by sending the packet to node 2. Node 2then forwards the packet to node 1 via pathway 236, where the packetexits the tunnel and is sent to node 0 on the original shortest path viapathway 206. If the secondary redundant tree also fails, in which casethere are two failures, the packet is dropped.

As discussed above, the shortest paths are utilized as the default pathsin a similar manner as the existing Not-via methodology. However, ifthere is a failure in a node or a link in the network, the node isplaced in a tunnel with a special IP address. By utilizing this specialaddress, a packet can avoid the failure. The packet may then exit thetunnel on the other side of the failure (i.e., at the next-next hop).

However, the pathways are computed in a different way than existingNot-via systems. The present invention utilizes maximally redundanttrees for forwarding if the packet must detour around a failed node orlink. Additionally, by utilizing these redundant trees, the use ofnumerous IP addresses is avoided since one pair of redundant trees canprotect multiple resources.

In two-node-connected networks, a pair of redundant trees routed at eachnode is determined. One of the redundant trees is designated the primarytree and the other tree is designated the secondary tree. If there is nofailure, packets follow the shortest path. If there is a failure in thenetwork, the next-next hop remains reachable by following one of the tworedundant trees. If it is possible, the packet is forwarded by followingthe primary tree rooted at the next-next hop. If it is not possible toforward the packet via the primary tree, the packet is forwarded via thesecondary tree. If a packet using the secondary path cannot beforwarded, then the packet is dropped as there must be at least twofailures in the network. With implementation of the present invention,the packets will reach the destination, even if there is one node or onelink failure. Furthermore, no loops can be formed because if a packetcannot be forwarded using the primary or secondary tree, the packet issimply dropped.

FIGS. 3A and 3B are flowcharts illustrating the steps of forwarding apacket where a node or link failure occurs in a network according to theteachings of the present invention. With reference to FIGS. 1-3, thesteps of the method will now be explained. In step 300, a packet istransported through the network 100 to a node. In step 302, it isdetermined if the node is the destination of the packet. If it isdetermined in step 302 that the node is the destination, it isdetermined if the packet is tunnelled in step 304. If it is determinedin step 304 that the packet is tunnelled, the packet exits the tunnel atthe destination node in step 306. However, in step 304, if it isdetermined that the packet is not tunnelled, the packet is processednormally in step 308.

In step 302, if it is determined that the node is not the destination,it is determined in step 310 if the address of the packet is a normaladdress. If it is determined that the address of the packet is a normaladdress, it is determined if the packet is forwarded on the shortestpath possible in step 312. If it is determined that the packet isforwarded on the shortest path possible, the packet is then forwarded onthe shortest path in step 314. However, if it is determined that thepacket is not forwarded on the shortest path possible, it is thendetermined if it is possible to forward the packet on a primaryredundant tree in step 316. If it is determined that it is possible toforward the packet on a primary redundant tree, the packet is forwardedon the primary redundant tree in step 318. If the packet is nottunnelled, the packet is dropped.

In step 310, if the address of the packet is not a normal address, it isdetermined if the packet is addressed on a primary redundant tree instep 320. If it is determined that the address of the packet is on aprimary redundant tree, it is determined if it is possible to forwardthe packet on a primary redundant tree in step 316. If it is determinedthat it is possible to forward the packet on a primary redundant tree,the packet is forwarded on the primarily redundant tree in step 318. Ifthe packet is not tunnelled, the packet is dropped.

In step 320, if it is determined that the packet is not addressed on aprimary redundant tree, it is determined if it is possible to forwardthe packet on a secondary redundant tree in step 322. If it isdetermined that it is not possible to forward the packet on thesecondary redundant tree, the packet is dropped in step 324.

In step 322, if it is determined that the packet can be forwarded on asecondary redundant route, the packet is forwarded on the secondaryredundant tree in step 326. If the packet is not tunnelled, the packetis put in a tunnel. Additionally, if necessary, the address of thepacket is changed to a tunnelled address.

The present invention does not require any modification to existingforwarding engines. In the present invention, three directed trees areneeded for each node as a root. The first tree is a shortest path tree.The second and third trees are the two redundant trees. Preferably, thesame trees at each node are utilized, which is possible if all the nodesuse the same topology. In some cases, when the algorithm finding a pairof redundant trees is not fully defined, more than one edge node may bechosen. However, priorities at nodes (for example, their loopback IPaddress can be such a priority) may be utilized to avoid problemsencountered where there is more than one node to choose.

In the present invention, addresses used for resilience are preferablydistinguished from normal addresses. The original Not-via has the sameproblem, but it is easy to solve, since addresses for resilience areonly used in the transport network. Thus, even private IP addresses maybe used. In this way, three addresses are assigned to each node. First,packets having a normal address as a destination are forwarded on theshortest path. Second, packets having the first detour address use theprimary redundant tree. Third, packets having the second detour addressuse the second redundant tree. Private IP addresses may be used for thetwo detour addresses (i.e., primary redundant tree and secondaryredundant tree). It should be understood that only three addresses pernode are necessary, but more than three addresses may still be used andremain in the scope of the present invention. The present invention maybe utilized in point-to-point networks with ring topology. In mostcases, the present invention does not need any new addresses at all.Normally, all the routers have a loopback address and at least twointerfaces, all having their own address. Thus, two of the interfaceaddresses may be used as detour addresses. In such a scenario, therouters are preferably addressed by their loopback addresses, otherwisepackets heading to the routers as destination (not the transportedtraffic) would not have fast reroute.

In existing Not-via solutions, other problems are encountered fornetworks containing LANs. Specifically, the capability of avoidingfailures in these networks significantly increases the number of IPaddresses needed. On the other hand, in the present invention, redundanttrees are utilized. Thus, LANs may be simply represented by a node ofthe graph on which the trees are computed. If a node representing a LANfails, the node may be easily avoided using one of the two redundanttrees. Furthermore, if a node connected to the LAN fails, one of theredundant trees remains connected. Since it is not necessary to assignany IP address to LANs because the LANs cannot be destinations, thepresent invention does not need an increase in the number of addresses.

With the present invention, many of the primary problems with existingNot-via addresses are eliminated. The number of IP addresses issignificantly reduced while the number of addresses is scaled linearlyto the number of nodes. Thus, the time needed to download the computedpaths to the line cards also decreases because of the use of a lowernumber of addresses. Furthermore, using redundant trees also eliminatesnumerous special cases utilized in existing Not-via systems.

In the present invention, to determine the redundant trees, an effectivealgorithm is necessary. Various algorithms may be utilized to find theredundant trees. For example, the redundant trees rooted at each nodemay be computed one node at time, which would take the time of n (thenumber of nodes) redundant tree computation. On the other hand, knowingthat whole redundant trees are not needed by any of the nodes in thenetwork, the nodes only need to know the next hops toward each root onboth of the trees, which opens the possibility of a faster algorithm. Byusing such an implementation, computational complexity is also reducedto the complexity of a single run of a Dijkstra's algorithm.

The present invention may also be implemented in not-two-node-connectednetworks. Although it is not possible for not-two-node-connectednetworks to find a pair of redundant trees, the network may still findmaximally redundant trees even in these graphs. A pair of maximumredundant trees is a generalization of redundant trees. If a pair ofmaximum redundant trees is given, their root node is reachable using anyof the trees. If the original graph was a ‘two-node-connected’, then apair of maximum redundant trees is a pair of redundant trees. Findingsuch trees may be accomplished in linear time. These trees can then beused to find the next hops of multiple trees.

The present invention may also be implemented in multiple-node-connectednetworks. In an n-edge-connected network (n>2), the network is atwo-node-connected as well, so the two redundant trees may still befound. If a link or node fails, it is possible to avoid the failure.Thus, the network may still transport the traffic and all the nodes withsufficient time to recognize the error. When all the nodes know the newtopology, the complete routing may be recomputed with rerouting as well.

The present invention may be utilized in any packet switched network andis not limited to an IP network. The present invention provides a fastreroute capability. The system employs maximally redundant trees asdetours in case of failures. The determination of a detour is providedby the destination address of the packet. Furthermore, if a packetcannot be forwarded using the default shortest path, the system mayutilize a tunnel to transmit the packet. The present invention does notrequire any new protocols as the existing link state routing protocolsmay be used.

The present invention provides many advantages over exiting Not-viasolutions. The present invention provides a very fast local reroutecapability in IP networks. The present invention provides a protectionto all links and nodes. Furthermore, loops are avoided since a packet isdiscarded if more than one failure is detected. The present inventionstill utilizes the shortest path as a default. The present inventionsignificantly decreases the time needed to compute the new paths anddownload the new paths to the line cards.

The present invention may of course, be carried out in other specificways than those herein set forth without departing from the essentialcharacteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1. A method of implementing lightweight Not-via Internet Protocol fastreroutes of a packet in a telecommunications network between a firstnode and a destination node, the method comprising the steps of:determining a shortest path between the first node and the destinationnode; determining a first maximally redundant tree and a secondmaximally redundant tree between the first node and the destinationnode, each of the first maximally redundant tree and the secondmaximally redundant tree providing an alternative path between the firstnode and the destination node, each alternative path having the leastnumber of nodes in common with the other alternative path; determiningif a failure exists between the first node and the destination node; andif no failure exists, sending the packet via the shortest path betweenthe first node and the destination node; if a failure exists, forwardingthe packet via the first maximally redundant tree after encapsulatingthe packet using a first type of special IP address, the first type ofspecial IP address identifying the destination node and designating thefirst maximally redundant tree as the active forwarding tree.
 2. Themethod according to claim 1 wherein if a failure exists and the firstmaximally redundant tree is not available, forwarding the packet via thesecond maximally redundant tree after encapsulating the packet using asecond type of special IP address, the second type of special IP addressidentifying the destination node and designating the second maximallyredundant tree as the active forwarding tree.
 3. The method according toclaim 2, wherein the method further comprises, upon determining that afailure exists and the first maximally redundant tree and the secondredundant trees are not available, dropping the packet.
 4. The methodaccording to claim 2 further comprising the step of calculatingnext-hops only in either the first maximally redundant tree or thesecond maximally redundant tree instead of calculating the completefirst maximally redundant tree or the complete second maximallyredundant tree.
 5. A system for implementing lightweight Not-viaInternet Protocol fast reroutes of a packet in a telecommunicationsnetwork, the system comprising: a first node for transmitting a packet;a destination node for receiving the packet; the first node having meansfor determining a shortest path between the first node and thedestination node; means for determining a first maximally redundant treeand a second maximally redundant tree between the first node and thedestination node, the first and second maximally redundant trees eachproviding an alternative path between the first node and the destinationnode, each alternative path having the least number of nodes in commonwith the other alternative path; means for determining if a failureexists between the first node and the destination node, wherein if nofailure exists, means for sending the packet via the shortest pathbetween the first node and the destination node; and if a failureexists, means for forwarding the packet via the first maximallyredundant tree after encapsulating the packet using a first type ofspecial IP address, the first type of special IP address identifying thedestination node and designating the first maximally redundant tree asthe active forwarding tree.
 6. The system according to claim 5 whereinif a failure exists and the first maximally redundant tree is notavailable, the system including means for forwarding the packet via thesecond maximally redundant tree after encapsulating the packet using asecond type of special IP address, the second type of special IP addressidentifying the destination node and designating the second maximallyredundant tree as the active forwarding tree.
 7. The system according toclaim 6, wherein the means for determining that a failure exists and thefirst maximally redundant tree and the second maximally redundant treesare not available, includes means for dropping the packet.
 8. The systemaccording to claim 5 further comprising calculation means forcalculating next-hops for either the first maximally redundant tree orthe second maximally tree, instead of calculating the complete firstmaximally redundant tree or the complete second maximally redundanttree.
 9. A node for implementing lightweight Not-via Internet Protocolfast reroutes of a packet in a telecommunications network from the nodeto a destination node, the node comprising: means for determining ashortest path between the node and the destination node; means fordetermining a first maximally redundant tree and a second maximallyredundant tree between the node and the destination node, the first andsecond maximally redundant trees each providing an alternative pathbetween the node and the destination node, each alternative path havingthe least number of nodes in common with the other alternative path; andmeans for determining if a failure exists between the node and thedestination node, wherein if no failure exists, means for sending thepacket via the shortest path between the node and the destination node,or if a failure exists, means for forwarding the packet via the firstmaximally redundant tree after encapsulating the packet using a firsttype of special IP address, the first type of special IP addressidentifying the destination node and designating the first maximallyredundant tree as the active forwarding tree.
 10. The node according toclaim 9, wherein if the means for forwarding the packet via the firstmaximally redundant tree is not available, the node further comprisesmeans for forwarding the packet via the second maximally redundant treeafter encapsulating the packet using a second type of special IPaddress, the second type of special IP address identifying thedestination node and designating the second maximally redundant tree asthe active forwarding tree.
 11. The node according to claim 9, whereinif it is determined that a failure exists and the first maximallyredundant tree and the second maximally redundant tree are notavailable, the node includes means for dropping the packet.
 12. The nodeaccording to claim 9, further comprising calculation means forcalculating next-hops for either the first maximally redundant tree orthe second maximally redundant tree, instead of calculating the completefirst maximally redundant tree or the complete second maximallyredundant tree.